Stability is of importance, with base precursors which can be put into practical use. Hence, great importance is attached to those base precursors which are stable and neutral at ordinary temperatures and which release a base only when heated. For example, stable compounds like urea are being used as described in U.S. Pat. No. 2,732,299, Belgian Pat. No. 625,554, etc.
Further, a technique of using urea of the ammonium salt of a weak acid (Japanese Pat. Publication No. 1699/65), a technique of using hexamethylenetetramine or semicarbazide (U.S. Pat. No. 3,157,503), a technique of using alkylamines, allylamines, etc. (Japanese Pat. Publication No. 8141/65), and the like, are known.
In addition, a technique of using hydrophobic guanidine derivatives (Japanese Patent Application (OPI) No. 45094/82) (The term "OPI" as used herein refers to a "published unexamined Japanese Patent Application") and a technique of using triazine compounds and carboxylic acids (U.S. Pat. No. 3,493,374) are also known.
Japanese Pat. Publication No. 18704/64 describes a technique of coating an acidic substance on soluble base particles, West German Pat. No. 119,516 describes a technique of encapsulating with wax, Japanese Pat. Publication No. 34792/64 and U.S. Pat. No. 3,284,201 describe a technique of forming a protective layer or an interlayer of a high molecular weight substance, Japanese Pat. Publication Nos. 2145/66, 2146/66, and 15466/66 describe a technique of forming a light-sensitive layer by dispersing in a binder using an organic solvent, and U.S. Pat. Nos. 3,653,091, 3,255,011, 3,294,534, 3,298,834 and 3,301,679, and French Pat. No. 1,405,427 describe a technique of using thermally decomposable acids.
Although various techniques as described above have been proposed, excellent techniques have not yet been attained. Because, light-sensitive materials using this type of compound capable of producing a base upon heating have poor preservability and fail to produce sufficient base upon being heated, thus failing to provide high image density. Further, thermal decomposition products such as colored products (e.g., tar) and white crystals are produced.